Re-etch process for color cathode-ray tube

ABSTRACT

AN APPARATUS FOR RE-ETCHING THE APERTUES OF A COLOR CATHODE-RAY TUBE SHADOW MASK TO INCREASE THE DIAMETER OF EACH APERTURE BY AN AMOUNT DEPENDENT UPON ITS SPACING FROM THE CENTER OF THE MASK. THE APPARATUS COMPRISES A TANK ADAPTED TO CONTAIN A FLUID ETCHANT SUITABLE FOR ATTACHING THE MASK MATERIAL, WITH CIRCULATING MEANS TO FLOW THE FLUID ETCHANT THROUGH THE MASK APERTURES AND BAFFLING MEANS TO DIRECT THE FLUID ETCHANT THROUGH THE APERTURES AT VELOCITIES WHICH DIFFER FROM APERTURE TO APERTURE AS A FUNCTION OF THE APERTURE SPACING FROM THE CENTER OF THE MASK.

L. DIETCH May 1, 1973 7 RE'ETCH PROCESS FOR ,COLOR CATHODERAY TUBE Filed May 5, 1971 1 lnvenior Leonard Dletch Attorney "United States Patent 3,730,809 RE-ETCH PROCESS FOR COLOR CATHODE-RAY TUBE Leonard Dietch, Skokie, Ill., assignor to Zenith Radio Corporation, Chicago, Ill. Filed May 3, 1971, Ser. No. 139,482 Int. Cl. C03c 15/00 US. Cl. 156-345 1 Claim ABSTRACT OF THE DISCLOSURE An apparatus for re-etching the apertures of a color cathode-ray tube shadow mask to increase the diameter of each aperture by an amount dependent upon its spacing from the center of the mask. The apparatus comprises a tank adapted to contain a fluid etchant suitable for attaching the mask material, with circulating means to flow the fluid etchant through the mask apertures and baffling means to direct the fluid etchant through the apertures at velocities which differ from aperture to aperture as a function of the aperture spacing from the center of the mask.

BACKGROUND OF THE INVENTION The subject invention concerns an apparatus for the processing of shadow mask color picture tubes which feature what has come to be known as re-etch. In accordance with such screening techniques, the shadow mask is originally etched and formed with apertures that are smaller in size than required for the mask as finally installed in the color tube but are dimensioned appropriately to use the mask in locating and dimensioning the phosphor dots of the screen. After screening has been accomplished, the mask is etched a second time, that is to say, it is re-etched to attain a hole size that is larger by a predetermined amount than the individual phosphor deposits. This screening technique is used in the fabrication of different types of color tubes, especially those which feature black-surround or post-deflection acceleration.

A black-surround tube of a preferred form is the subject of Pat. No. 3,146,368 issued Aug. 24, 1964 in the name of Joseph P. Fiore et al. and assigned to the assignee of the present invention. It differs from conventional shadow mask types of cathode ray tubes in two material respects: (1) each phosphor dot of the screen is surrounded by a material, such as graphite, that is absorptive of light, and (2) its electron beam is larger than the diameter of the phosphor dots. A post-deflection focus or post-deflection acceleration color tube differs from the conventional shadow mask device in that additional beam focusing is accomplished between the center of deflection and the screen. Because of the added focusing, more beam current impinges upon the screen than otherwise and it is necessary, because of the post-deflection focusing, that the phosphor dots be smaller than the apertures of the mask. As stated above, in this respect, it is similar to the black-surround-tube.

The concept of establishing apertures in the shadow mask of a relatively small size to accommodate the mask for use in printing of the screen and then enlarging the apertures after screening and before final installation of the mask into the tube is indeed well known. In prior proposals, the mask blank is originally etched to have apertures of a desired final size and the apertures are then temporarily filled with a removable material in order to step down the aperture size for screening purposes. As a matter of practice, this approach is found to have serious difficulties including, among others, non-uniformities of the phosphor dots obtained in the screening process.

In a preferred approach, the technique of re-etching or etchback as described above is practiced because it affords a materially greater degree of precision in dimensioning of the phosphor dots of the screen, and also distinctly superior results from the standpoint of uniformity of the phosphor deposit.

It has been discovered that by grading the final aperture sizes, that is to say, by making the apertures in the center area larger than the apertures at the edges of the mask, improved color reproduction can be attained. The present invention takes full advantage of the inherent features of the re-etch process by providing an apparatus for producing an aperture mask where the aperture sizes are graded to make possible such improved color reproduction.

Accordingly, it is an object of the invention to provide an apparatus for re-etching the apertures of a color cathode-ray tube shadow mask to increase the diameter of each aperture by an amount dependent upon its spacing from the center of the mask.

SUMMARY OF THE INVENTION The present invention provides an apparatus for reetching the apertures of a cathode ray tube shadow mask to increase the diameter of each aperture by an amount dependent upon its spacing from the center of the mask. The apparatus comprises a tank adapted to contain a fluid etchant suitable for attacking the mask material, with circulating means to flow the fluid etchant through the mask apertures and baffling means to direct the fluid etchant through the apertures at velocities which differ from aperture to aperture as a function of the aperture spacing from the center of the mask.

DESCRIPTION OF THE DRAWING The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in which the single figure is a side view, partly in cross-section, of a re-etch apparatus which may be used to practice the present invention.

The present invention finds particular application in practicing the process disclosed and claimed in copending application Ser. No. 168,223, filed Aug. 2, 1971, in the name of James W. Schwartz and assigned to the assignee of the present invention.

Referring now to the figure, shadow mask 1 is disposed in tank 2 with its convex side pointed downwardly. The shadow mask 1 rests on and is supported by mounting ring 3. The tank 2 contains a fluid etchant 4 which is typically a solution of ferric chloride suitable for attacking the cold rolled steel material of shadow mask 1. The etchant 4 is circulated through the tank by pump 5 which pumps the etchant out of the bottom of the tank through outlet 6. The etchant is then pumped through line 7 to distributing line 8 where it is reintroduced into the tank through inlets 9. In the figure, only two inlets are shown but actually any number can be employed to obtain the desired circulating rate of the etchant.

Mounting ring 3 is preferably shaped to conform to the inner dimensions of the tank .2 and the outer dimensions of the shadow mask 1 to force all of the etchant to circulate through the mask apertures 10 of shadow mask 1.

As shown, the shadow mask is disposed horizontally but may be disposed in any plane so long as the etchant can flow freely through the apertures 10.

The re-etch apparatus as thus far described is suitable for uniformly re-etching the apertures across the aperture field of the mask. The increase in the diameter of each aperture by an amount dependent upon its spacing from the center mask 1 is accomplished by controlling the velocity of etchant flow through the apertures to differ from aperture to aperture as a function of the spacing. This is achieved by bafile 20 which rests on bracket 21 and is disposed between inlets 9 and shadow mask 10. The bafiie 20 is held onto brackets 21 by gravity and can be easily removed for mounting the shadow mask 10 in its position on mounting ring 3. Once the mask is in place, the baflle is placed back onto bracket 21.

Of course, difierent bame configurations cane be chosen to meet particular aperture size-center spacing requirements. \As depicted in the figure, the baffie 20 is a single element, but multiple-element bafiiing systems may be employed. The bafiiing system may be designed in accordance with well-known principles of fluid mechanics, but as a practical matter empirical design approaches are ordinarily employed.

The velocity of the etchant 4 is affected by the baffle as represented by the arrows 30. The etchant flows at a much slower rate at the peripheral areas 22, 23 of the shadow mask 10 than at the center area 24, resulting in less etching of the apertures at the outer portions of the aperture field than at the center. Therefore, the diameters of the apertures gradually decrease from the center 24 of mask 10 to the edges 22, 23.

The present invention has all of the advantages of the re-etching processes previously described with the added feature of increasing the diameter of each aperture by an amount dependent upon its spacing from the center of the mask. By properly controlling the rate at which the etchant flows through each aperture, any aperture diameter and spacing relationship may be obtained.

While a particular embodiment of the invention has been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. An apparatus for re-etching the apertures of a color cathode-ray tube shadow mask to increase the diameter of each aperture by an amount dependent upon its spacing from the center of said mask, comprising:

a tank for containing a liquid etchant suitable for attacking the shadow mask material; circulating means to flow said liquid etchant thru said mask apertures; means for supporting said mask within said tank spaced around said mask; and

baffling means supported adjacent to said mask supporting means for directing said fluid etchant through said apertures at velocities which difier from aperture to aperture as a function of said spacing.

References Cited UNITED STATES PATENTS 3,447,985 6/1969 Seitz 156345 3,549,439 12/1970 Kaveggia et al. 156-345 J. H. STEINBERG, Primary Examiner US. Cl. X.R. 

